Tic tac toe - assembly x86_16 🚧

Instructions

How to run

This program should be executed in Windows using DosBox environment

• Compile main.asm using NASM as we did on the labs:

nasm main

• Link .o files using freelink:

freelink main

• Run the game:

main

How to play

It starts in a black screen. This screen wait for an input from your keyboard. Whatever the input, the screen remains black unless you type "s" or "c".

• "s" is for close the game
• "c" is for start the game

When the game starts, you'll see a screen like this:

It has 2 options to play:

• X
• C

The character C represents the circle.

The move should has 3 characters:

• symbol (X/C)
• line (1, 2 or 3)
• column (1, 2 or 3)

and the move happens when you type the ENTER key

For example: X11 generates the move below:

• You can't move over a held position or play with the same symbol twice. If you do this, a message will appear on the screen and your move won't be processed.

• There's a case which it gets a buffer overflow. In this case, a message will appear on the screen and your input won't be processed. You can delete all the characters and type again, or delete one character and type ENTER to print the wrong command and reset the buffer.

When the game ends, a message will appear on the screen showing the winner if is the case. Wait a time and a message "press any key to close" will appear and you exit the game.

Implementation details

Player moves and board masks

Each playe move and all the positions that have already been played are represented as 2 bytes, where the least significant 9 bytes represent the positions on the board.

If the bit on the position is set to 1, that means that position has been played by one of the players. The same idea applies for each player move.

Representation:

We represent the player moves as well as the board positions as follows:

Look the image table.png

board/moves: 0000000x.xxxxxxxx

So, we can figure out if a player has won the match or if the board if full by means of some masks. Let's define them:

Board is full:

If the board is full, that means all the 9 least significant bytes are 1, meaning all positions have been taken, so let's define a mask for that:

board full mask: 00000001.11111111 => 0x01ff

Player won with sequence 012:

won 012 mask: 00000000.00000111 => 0x0007

Player won with sequence 345:

won 345 mask: 00000000.00111000 => 0x0038

Player won with sequence 678:

won 678 mask: 00000001.11000000 => 0x01C0

Player won with sequence 048:

won 048 mask: 00000001.00010001 => 0x0111

Player won with sequence 642:

won 642 mask: 00000000.01010100 => 0x0054

Player won with sequence 630:

won 630 mask: 00000000.01001001 => 0x0049

Player won with sequence 741:

won 741 mask: 00000000.10010010 => 0x0092

Player won with sequence 852:

won 852 mask: 00000001.00100100 => 0x0124